It is a known fact that for heating a room, convection heat, due to its more even distribution of the heat over the space of the room to be heated, is much more efficient and agreeable than radiant heat. That is why in front of a radiant heater, such as an open hearth fire, a radiating gas fire, an electric radiant heater or other source of radiant heat, screens have already been placed which are well adapted for such a radiant to convection heat conversion. Generally, such screens consist of a row of interconnected (at least with their upper portions), spaced apart vertical pipes having at or near their lower end an inlet opening and at or near their upper end an outlet opening. When such pipes are heated by the radiant heat received on their outer surfaces the air inside them is heated and flows as a result of the chimney-action of the pipes upwards, so that continuously cool air is sucked from the room through the low inlet openings into the pipes and hot air is discharged through the high outlet openings of the pipes back into the room where it is distributed by circulation.
However, screens of this kind have to satisfy several requirements. They must be easily manageable and quickly heatable. This means that the pipes and the coupling means for their interconnection must be constructed as light as possible, and in any case the pipes which contribute to the major part of the weight of the screen must have a very thin wall (some tenths of a millimeter). But such pipes are easily damaged so that great care must be taken with the manner in which the pipes are interconnected. Furthermore, these screens can be an obstacle in the room, so that they must be adapted to be put easily away and stored. This requirement can be satisfied by making the screen foldable, which requires the provision of a hinge joint between the pipes of at least one pair but preferably of several or all pairs of adjacent pipes of the screen. When the pipes have a very thin wall much care must be taken with the manner in which the hinge joint is constructed and is attached to the pipes.
Now, a screen, e.g. a fire-guard used also as a screen to prevent sparks or other small particles of combustion from entering the room in which it is placed in front of an open hearth fire, of the above-mentioned construction and satisfying the noted requirements has been disclosed in European patent specification EP-A-0 123 342. This known screen comprises a row of interconnected) at least for a part of their length), horizontally spaced apart, round pipes which extend vertically, are placed side by side and have each at or near their lower end an opening to admit air from and at or near their upper end an opening to discharge air into the room to be heated by the source of heat. The two pipes of at least one pair of adjacent pipes of this known screen are so interconnected by a hinge joint as to ensure that one pipe of the pair is adapted to swing with its longitudinal axis in a circular cylinder surface about the longitudinal axis of the other pipe of the pair. This hinge joint consists of a splitted ring and connecting parts interconnecting the ring parts and also of means for so clamping the connecting parts towards one another, as to guarantee that in the active end condition of the clamping means one ring part of the coupling member is firmly clamped on one pipe, but the other ring part embraces the other pipe in a manner as to allow still a relative rotation of the ring part and the other pipe.
In addition to the fact that a screen of this type satisfies the above-mentioned requirements, it has the advantage that it is continually cooled by the current of air in the pipes, so that one will not burn oneself when touching it.